2 Optics Sources W-3 -4

8/11/2019 2 Optics Sources W-3 -4

1/53

UVX-rays IR

Micro

Waves Radio/Televisionwavesg

- rays

Wavelength (m) 10-910-10 10-8 10-7 10-6 10-310-5 10-4 10110-110-2 1

Wave number cm-1108 107 106 105 104 103 102 101 1 10-1 10-2 10-3

700600400


2/53


3/53

Electromagnetic Spectrum

(m)

1000 100 10 1 0.1 0.01

ultraviolet

visible

lightinfraredmicrowaves x-rays

High

Energy

Low

Energy


4/53

Sources of EMR

Deuterium Lamp UV

Mercury lamp UV

Xenon lamp UV-VIS

Tungsten Lamp VIS-NIR

Silicon carbide globar

Nernst

IR

Laser UV-VIS-NIR

Hollow-cathode lamp UV-VIS-NIR

Flame ,Furnaces, Plasmas UV- VIS-IR

X-ray tube X-Rays


5/53

A general rule:

The higher an objects temperature, the more intenselythe object emits electromagnetic radiation and theshorter the wavelength at which emits most strongly

Radiation depending on Temperature

The example of heated iron bar.As the temperature increases

The bar glows morebrightly

The color of the bar alsochanges


6/53

The black body is important in thermal radiation theory

and practice.

The ideal black body notion is important in studyingthermal radiation and electromagnetic radiationtransfer in all wavelength bands.

The black body is used as a standard with which the

absorption of real bodies is compared.


7/53

Definition of a black body

A black body is an ideal body whichallows the whole of the incident

radiation to pass into itself (without

reflecting the energy ) and absorbs

within itself this whole incident

radiation. This propety is valid for

radiation corresponding to all

wavelengths and to all angels of

incidence. Therefore, the black body

is an ideal absorber of incidentradaition.


8/53

A blackbody is a hypothetical objectthat is a perfect absorber of

electromagnetic radiation at allwavelengths

The radiation of a blackbody isentirely the result of itstemperature

A blackbody does not reflect anylight at all

Blackbody curve: the intensities ofradiation emitted at variouswavelengths by a blackbody at agiven temperature

The higher the temperature, theshorter the peak wavelength

The higher the temperature, thehigher the intensity

Blackbody Radiation

Blackbody curve


9/53


10/53

Basic Laws of Radiation

1) All objects emit radiant energy.

2) Hotter objects emit more energy than colder

objects (per unit area). The amount of energy

radiated is proportional to the temperature of

the object.

3) The hotter the object, the shorter the

wavelength () of emitted energy.

This isWiens Law

max 3000 m

T(K)


11/53

Stefan Boltzmann Law.

F = T4

F = flux of energy (W/m2)

T = temperature (K)

= 5.67 x 10

-8

W/m

2

K

4

(a constant)

Wiens Law

max 3000 m

T(K)


12/53

We can use these equations to calculate properties

of energy radiating from the Sun and the Earth.

6,000 K 300 K


13/53

T(K)

max

(m)

region inspectrum F

(W/m2)

Sun 6000 0.5 Visible 7 x 107

Earth 300 10 infrared 460


14/53

Temperature Source

1,700 K Match flame

1,850 K Candle flame, sunset/sunrise

2,7003,300 K Incandescent lamps

3,000 K Soft White CFL

3,200 K Studio lamps, photo floods lights.

3,350 K Studio "CP" light

4,1004,150 K Moonlight

5,000 K Horizon daylight

5,000 K

tubular fluorescent lamps or cool

white/daylight compact fluorescent

lamps (CFL)

5,5006,000 K electronic flash

6,200 K Xenon arc lamp

6,500 K Daylight

5,50010,500 K LCD or CRT screen


15/53


16/53

Light bulbs contain a metal wire filament,

which is heated by electricity. The filament

becomes so hot, it glows white. The change from electrical energy to

visible light energy involves the following

energy transformation:Electrical energy -> thermal energy -> visible

light energy

Incandescent sources


17/53

Spectral Lines

Bright spectrum lines can be seen when a chemicalsubstance is heated and valoprized (Kirchhoff, ~1850)


18/53

Kirchhoffs Laws on Spectrum

Law 1- Continuous spectrum: a hot opaque body, such as

a perfect blackbody, produce a continuous spectrum

acomplete rainbow of colors without any spectral line

Law 2 emission line spectrum: a hot, transparent gasproduces an emission line spectrum a series of bright

spectral lines against a dark background

Law 3 absorption line spectrum: a relatively cool,transparent gas in front of a source of a continuous

spectrum produces an absorption line spectrum aseries of dark spectral lines amongst the colors of thecontinuous spectrum. Further, the dark lines of aparticular gas occur at exactly the same wavelengthas the bright lines of that same gas.


19/53

Each chemical element has its own unique set of spectral lines.


20/53

Kirchhoffs Laws on Spectrum

Three different spectrum: continuous spectrum, emission-linespectrum, and absorption line spectrum


21/53

Electrons occupy

only certain orbits orenergy levels

When an electronjumps from one orbit

to another, it emits orabsorbs a photon ofappropriate energy.

The energy of the

photon equals thedifference in energybetween the twoorbits.

Bohrs Model of Atom

Bohrs Model of Hydrogen


22/53

Deuterium Arc Lamp

Li ht


23/53

Light sources

Black-body radiation for vis and IR but not UV

- a tungs ten lampis an excellent source of black-body radiation

- operates at 3000 K

- produces from 320 to 2500 nm

For UV:

- a common lamp is a deuterium arc lamp

- electric discharge causes D2 to dissociate and emit UV radiation (160 325

nm)

- other good sources are:Xe (250 1000 nm)

Hg (280 1400 nm)


24/53

D2 Lamps

Type of lamp is used for Ultraviolet Spectroscopy most bulbs mainly show visible light and the intensity

of UV light is very small

D2 lamp, the intensity of the UV light is very high,

Which leads to a better signal to noise ratio for measurements with UV light

Emits wavelengths from 160 nm to 400 nm

Deuterium is stored a controlled pressures


25/53

A deuterium lamp uses

a tungsten filament and anode placed on

opposite sides of a nickel box structure

designed to produce the best output

spectrum.

Unlike an incandescent bulb, the filament

is not the source of light in deuterium

lamps. An arc is created from the filament

to the anode

Since the filament must be very hot

before it can operate, it is heated for

approximately twenty seconds before

use.

Because the discharge process produces

its own heat, the heater is turned down

after discharge begins


26/53


27/53

D

2

lamp


28/53


29/53

Window Material

UV Glass Synthetic Quartz Synthetic Silica MgF2

Minimum wavelength

115nm, 160 nm, 185 nm

Maximum wavelength

Typically around 400 nm


30/53


31/53

a tungsten anode and a cylindrical cathodeneon or argon at a pressure of 1 to 5 torr

The cathode is constructed of the metal whose

spectrum is desired or served to support a layer of

that metal

Hollow Cathode Lamp


32/53

Ne or Ar

at 1-5

Torr


33/53


34/53

Ionize the inert gas at a potential of ~ 300 V

Generate a current of ~ 5 to 15 mA as ions andelectrons migrate to the electrodes.

The gaseous cations acquire enough kinetic energy to

dislodge some of the metal atoms from the cathodesurface and produce an atomic cloud.

A portion of sputtered metal atoms is in excited states

and thus emits their characteristic radiation as they

return to the ground sate

Eventually, the metal atoms diffuse back to the cathodesurface or to the glass walls of the tube and are re-

deposited

Hollow Cathode Lamp


35/53

Infrared Sources


36/53

Infrared Sources

Most Common IR Sources

Nernst glower

cylinder of rare-earth oxides

glowbar

silicon carbide rod

50mm long by 5mm diameter

incandescent wire

nichrome wire


37/53

Infrared Sources

Special Application IR Sources

mercury arc

far-infrared tungsten filament

near-infrared

carbon dioxide laser tunable

Th N t l


38/53

The Nernst glower

Typically it is in the form of a cylindrical rod or tube havinga diameter of 1-2 mm and length of 20 mm sealed by a

platinum leads to the ends to permit electrical connection.

It is composed of a mixture of rare earth oxides such aszirconium oxide (ZrO2), yttrium oxide (Y2O3) and erbiumoxide (Er2O3) at a ratio of 90:7:3 by weight.

They are operated by being electrically heated to about1500 to 2000 C. Initially they required external heatingbecause the material is an insulator at room temperature.

Operates best in wavelengths from 2 to 14 micrometers

Produces black body radiation


39/53

The Nernst glower

Nernst glowers are fragile.

They have a large negative temperature coefficient ofelectrical resistance and must be preheated to beconductive.

Resistance decreases with increasing temperature thesource circuit must be designed to limit the current toprevent rapid heating and destroying the source
http://www.google.ps/imgres?imgurl=http://www.nernst.de/museum/glower.jpg&imgrefurl=http://www.nernst.de/museum/museum.htm&usg=__qtJc3Z7sz51nCAjHqsHPzfzsOaw=&h=455&w=1289&sz=142&hl=ar&start=4&zoom=1&um=1&itbs=1&tbnid=Y8cKH9odkXcjsM:&tbnh=53&tbnw=150&prev=/search%3Fq%3Dnernst%2Bglower,%2Bir%2Bsource%26tbnid%3Dv6CsEFAWhRnHvM:%26tbnh%3D0%26tbnw%3D0%26um%3D1%26hl%3Dar%26rlz%3D1W1AMSA_en%26biw%3D1366%26bih%3D492%26tbm%3Disch&ei=9s5WTv-4M4qv8gPSnLTFDA


40/53

Incandescent Wire Source

Lower intensity IR source butlonger life than the Globar orNernst glower.

A tightly wound spiral of nichromewire heated to about 1100 k by anelectric current.

A similar source is a rhodium wireheater sealed in a ceramiccylinder.

Incandescent wire sources are

longer lasting but of lowerintensity than the glower or globar.


41/53

The Tungsten Filament Lamp

Ordinary tungsten filament lamp (A

quartz halogen lamp contains atungsten wire filament and iodinevapor sealed in a quartz envelope orbulb), used for near IR region of 4000-12,800 cm-1 (2.5-0.78m)

In a standard tungsten filament lamp,

the tungsten evaporates from thefilament and deposits on the lampwall.

This process reduces the light outputas a result of the black deposit on thewall and the thinner filament.

The halogen gas in a tungsten-halogen lamp removes theevaporated tungsten and redepositsit on the filament, increasing the lightoutput and source stability


42/53

Spectrum of Tungsten lamp


43/53

Globar

Globar is a silicon carbide rod of 5 to 10 mm width and

20 to 50 mm length which is electrically heated up to

1,000 to 1,650 C


44/53


45/53

Nernst Glower vs. Globar

The two light sources are similar in many ways, such

as the function and temperature range.

However, the Nernst glower is better used at shorter

IR wavelengths (near IR), whereas globar is better

used at longer IR wavelengths.


46/53

Advantages of Nernst

Requires less power than a globar

Lasts a lifetime

Operates in air


47/53

Disadvantages

Very expensive

Extremely fragile

Because it is operated in the air, whichis an advantage, if the temperature

becomes too high, it will burn out, which

is obviously a disadvantage.


48/53
http://www.google.ps/imgres?imgurl=http://www.modulatedlight.org/Modulated_Light_DX/LampMods.jpg&imgrefurl=http://www.modulatedlight.org/Modulated_Light_DX/LongArticle1Jan79.html&usg=__jZlKIFSvuAY-8kmIAgOt_P0NgV4=&h=479&w=391&sz=12&hl=ar&start=1&zoom=1&um=1&itbs=1&tbnid=8BFMZjR2pPAt8M:&tbnh=129&tbnw=105&prev=/search%3Fq%3Dmercury%2Barc%2Blamp,%2BIR%2Bsource%26tbnid%3D8BFMZjR2pPAt8M:%26tbnh%3D0%26tbnw%3D0%26um%3D1%26hl%3Dar%26sa%3DX%26rlz%3D1W1AMSA_en%26biw%3D1366%26bih%3D492%26imgtype%3Di_similar%26tbm%3Disch&ei=UdFWTrHdFJC38QPNkcm6DA


49/53

The Mercury Arc.

Used for Far IR region (>50 m).

It is a high pressure mercury arc

which consist of a quartz - jacketedtube containing Hg vapor at P > 1atm.

When current passes through thelamp, mercury is vaporized, excited,

and ionized, forming a plasmadischarge at high pressure (P>1 atm)

In the UV and visible regions, this

lamp emits atomic Hg emission linesthat are very narrow and discrete, butemits an intense continuum in the far-IR region.
http://www.google.ps/imgres?imgurl=http://www.modulatedlight.org/Modulated_Light_DX/LampMods.jpg&imgrefurl=http://www.modulatedlight.org/Modulated_Light_DX/LongArticle1Jan79.html&usg=__jZlKIFSvuAY-8kmIAgOt_P0NgV4=&h=479&w=391&sz=12&hl=ar&start=1&zoom=1&um=1&itbs=1&tbnid=8BFMZjR2pPAt8M:&tbnh=129&tbnw=105&prev=/search%3Fq%3Dmercury%2Barc%2Blamp,%2BIR%2Bsource%26tbnid%3D8BFMZjR2pPAt8M:%26tbnh%3D0%26tbnw%3D0%26um%3D1%26hl%3Dar%26sa%3DX%26rlz%3D1W1AMSA_en%26biw%3D1366%26bih%3D492%26imgtype%3Di_similar%26tbm%3Disch&ei=UdFWTrHdFJC38QPNkcm6DA


50/53

Hg Lamp Spectrum

Wavelength (nm) Name Color

365.4 I-line ultraviolet (UVA)

404.7 H-line violet

435.8 G-line blue

546.1 green

578.2 yellow-orange


51/53

Summery of different IR sources


52/53

IR Laser Sources


53/53

IR Laser Sources

A laser is a light source that emits very intense

monochromatic radiation.

Some lasers, called tunable lasers, emit more than onewavelength of light, but each wavelength emitted ismonochromatic.

The combination of high intensity and narrow line widthmakes lasers ideal light sources for some applications.

Two types of IR lasers are available: gas phase and solid-state.

2 Optics Sources W-3 -4

Documents